Nothing as eye-catching as a duck island emerged yesterday, when the Treasury's Coins public expenditure database was made public. Some bizarre line from among the millions in the ledger may yet come to symbolise the haphazard manner in which public funds are occasionally spent. The real point, however, is not the release of any one informational pebble; the point is that a full mountain of data is, very slowly, coming into view.

To make good on its promised right to data, the coalition will have to make further, more detailed and more informative releases than yesterday's, until the point where it is possible to establish where, when and how every last pound is being spent. Some obvious questions are raised, for example about whether resources are skewed towards marginal seats, but others will form only as the mining of the information reveals unexpected connections. In this sense, the terra incognita of the human genome is a more telling precedent than the records of MPs' expenses, where dodgy claims were – quite predictably – the only thing to watch.

Former Labour ministers can protest, as Jim Knight did yesterday, that the open government programme is little more than a "rebranding" of what they were already doing. Certainly, as a matter of policy, Labour had reversed the old presumption that data should remain under wraps unless there was a good reason why it should not. But government policy is not always the same as government practice and, as recently as March, Whitehall was actively fighting off freedom of information requests to release Coins. While the coalition is naturally keen to explain its disclosure in terms of high principle, only the naive will doubt that self-interest is playing a role here as well. If and when unpopular lines of expenditure catch the public eye, all the red faces will be on the red side of parliament where the purse strings were controlled until recently. A measure of outrage about wasteful expenditure is also a positive help in preparing the way for the tough spending round due in the autumn. Perhaps David Cameron, who made great play with one department's heavy expenditure on flowers at his first prime minister's questions this week, has studied how Lord Rothermere's anti-waste league prepared the political ground for the swinging of the axe on public finances in the 1920s.

Taken together with asymmetric Tory plans to hand local electorates a veto on tax rises but not service cuts, the prospect of line-by-line scrutiny of state expenditure is not an entirely comfortable one for advocates of the public realm. If the debate becomes one in which the people are asked to chuck out public programmes in the same manner that they might vote contestants out of the Big Brother house, it will be tough to explain why taxpayer money has to be spent on NHS computers as well as NHS nurses, and even tougher to defend costly interventions that aim to give young offenders a second chance. Democracy, however, is a messy business, and in the end there is no alternative apart from making the case and entrusting it to the people's good sense. In America, where the free flow of information is more deeply entrenched, detailed mapping of the costs of incarceration has been used to make the point that taxpayers' money is already being spent in poor neighbourhoods, but that it is being spent on the wrong things.

A forward-looking left must go with the tide of transparency, not attempt to swim against it. We learned yesterday that the government spent £1.8bn on consultants last year, but we did not learn which ones: the veil of commercial confidentiality continues to block out the light as reliably as the blanket of national security. The people's money should not be spent away from public view. With PFI and privatisation, the grey area between public and private has grown wider than ever before. This no man's land is crying out for a blast of the light.